Glow plug for internal-combustion engines



May 9, 1950 Elg l- E. J. BENTZ ET AL GLOW PLUG FOR INTERNALCOMBUSTION ENGINES Filed July 19, 1948 I \l B l (I I IN V EN TORS.

AT T ORNEY Patented May 9, 1950 GLOW PLUG FOR INTERNAL-COMBUSTION ENGINES Erwin .l. Bentz, Washington, and Kenneth J.

Fleck, Peoria, 111., assignors to Caterpillar Tractor 00., Peoria, Ill., a corporation of California Application July 19, 1948, Serial No. 39,408

1 Claim. 1

This invention relates to glow plugs of the kind employed in the combustion chamber of a compression ignition engine.

Due to the difficulty of starting a compression ignition engine particularly at low atmospheric temperatures, it is conventional practice to associate a glow plug with each of the working cylinders to aid in initiating combustion. Such plugs comprise a resistance element adapted to be energized from an electric storage battery or the like causing the resistance element to be heated to a high temperature facilitating ignition of the mixture of fuel and air in the cylinder. Although the glow plugs are energized only during the starting period, it is necessary that they be able to withstand the high temperatures and pressure, as well as corrosive action of the combustion process encountered during normal engine operation.

One of the principal difficulties encountered in obtaining a satisfactory glow plug has been that of obtaining a resistance element of sufiicient size and strength to withstand the conditions prevailing in a combustion chamber without requiring an excessive amount of electrica1 energy when energized from a standard automotive storage battery. It has been the practice in the past to connect a number of such plugs in series, thereby reducing the voltage drop across each plug permitting the use of materially larger resistance elements having the same energy requirements. However, when a plurality of plugs are connected in series, failure of one plu results in failure of the other plugs in the series.

It is, therefore, an object of the present invention to provide a glow plug of improved construction that overcomes the above mentioned dilficulties. A further object is to provide a glow plug with the resistance element in a protective cap which is heated by conductance to a temperature sufiicient to ignite fuel and air mixture. Qther and more specific objects and advantages of this invention are made apparent in the following specification in which reference is made to the accompanying drawings.

In the drawings:

Fig. 1 is a fragmentary sectional view through the combustion chamber of a compression ignition engine illustrating a glow plug in association therewith,

Fig. 2 is a central longitudinal sectional view through a glow plug embodying the present invention,

Fig. 3 is an enlarged fragmentary sectional view illustrating in detail the manner in which the resistance element is associated with the protecting cap, and

Fig. 4. is an elevation of a part of a glow plug illustrating a modified form of this invention,

In Fig. l, a portion of a conventional type of compression ignition engine is shown in which one of the cylinders is illustrated at IU as containing a piston il, disposed for reciprocation therein. The upper end of the cylinder is closed by means of a cylinder head, a portion of which is illustrated at 3 as provided with a suitable opening for the reception of a burner tube 14. The burner tube is adapted to receive a fuel injector l5 which is supplied with fuel under pressure from a metering pump (not shown) by means or a fuel line l6. Fuel from the fuel valve i5 is sprayed into a precombustion chamber ll, provided. in the burner tube where it is ignited by contact with the high temperature compressed air within the chamber l7.

When starting the engine, especially at low atmospheric temperatures, it is diflicidt to heat the air within the precomcustion chamber by compression alone to a high enough temperature to ignite the fuel. This difliculty is overcome by a glow plug it, one end of which extends into the precomhustion chamber having a threaded connection therewith and the opposite end of which is connected by a suitable conductor 59 to a storage battery or the like (not shown). A circuit is completed by grounding to the engine and the vehicle in a conventional manner. When energized, the end of the glow plug extending into the precombustion chamber is heated to raise the temperature of the surrounding mixture of fuel and air. It is to the construction of the glow plug that this invention is directed.

As illustrated in Fig. 2, the glow plug comprises an outer shell 20, having an axial bore 2| for the reception of an electrode 22. The electrode has a threaded connection with an insulator 23 disposed within a suitable counterbore provided in the shell and the insulator is retained therein by deforming the adjacent end of the shell as illustrated. At its extending end, the electrode 22 is adapted to receive the electrical conductor 19 secured by means of a pair of lock nuts 24 and 25.

As is best illustrated in Fig. 3, the opposite end of the electrode carries a resistance coil 26 with one end secured to the electrode as by brazing and its opposite end secured as by welding to the closed end of a cap 28. The open end of the cap 28 is received in a suitable counterbore provided in the outer shell and may be retained therein as by brazing. The resistance element 26 is completely enclosed by the cap 28 preventing contact with combustion gases thus permitting it to be made of any desired material and size to give optimum performance. A sleeve 29 of mica or other dielectric material highly resistant to heat is interposed between the resistance coil and the side wall of the cap serving as an insulator to prevent the electric current from being grounded to the cap before it has traveled through the entire length of the coil.

It is desirable that the coil 26 be assembled as close as possible to the inner wall of the protecting cap 28 to facilitate free transferof heat to the cap. This closeness of assembly may be obtained by permitting the natural resiliency of the wire-like stock of which the coil is made to expand the coil outwardly toward the wall of the cap. This is accomplished in production, first, by forming the coil to a diameter slightly larger than the inside diameter of the cap; then constricting its diameter within its resilient limits as by twisting the coil around a small cylindrical mandrel. The mandrel is preferably threaded to receive the separate turns of the coil and retain them in their normal separated positions. The mandrel with the coil thus twisted upon it and reduced in diameter is inserted in the cap and the coil is then released to expand, freeing itself from the mandrel and exerting an outward pressure against the insulating sleeve 29. The coils are insulated from each other as by any suitable material indicated at 30 having satisfactory electrical insulating characteristics as well as good heat conducting characteristics such as powdered aluminum oxide. By using a conical ended tool for packing this material into the cap, the coils of the resistance element are urged outwardly against the sleeve 29, as well as downwardly, thus providing progressively less space between adjacent coils nearest the closed end of the cap. This is particularly desirable in that it provides a greater number of coils in the end of the cap thus achieving more rapid and intense heating in this area. The insulation is held in place by a suitable cement forming a cap 3|, which upon hardening, not only prevents the insulation from escaping from the cap but forms a centering support for the electrode 22.

In operation, the cap 28, which is in direct contact with the gases in the combustion chamber, is heated to a high temperature by conducted heat from the resistance coil 26 insuring ignition of the combustible mixture. As the resistance coil is protected from contact with the gases of combustion in the chamber by the cap 28, it may be made from any suitable material and of a size requiring a minimum of electrical current to energize, resulting in improved performance. As it is only the cap 28 which is in contact with the combustion gases, the life of the glow plug is materially extended.

Fig. 4 illustrates a modified form of this glow plug in which the cap 28 enclosing the resistance element is provided with a domed end closure. This domed construction increases the strength and rigidity of this part and may be preferred in some installations in which increased strength is required.

We claim: 7

A glow plug for use in an engine combustion chamber which comprises an electrically heated resistance element and a protective shield enclosing said element in heat conducting relationship thereto, and electrical insulation between the shield and element throughout substantially the entire area of the element said resistance element being formed as a cylindrical coil with a normal diameter greater than the interior of the protective shield whereby it will have a resilient tendency to expand outwardly toward said shield.

ERWIN J. BENTZ. KENNETH J. FLECK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,453,461 Hoffman May 1, 1923 1,457,690 Brine June 5, 1923 1,590,891 Heany June 29, 1926 2,130,365 Paulson Sept. 20, 1938 2,287,295 Cox et a1 June 23, 1942 FOREIGN PATENTS Number Country Date 315,830 Germany Nov. 13, 1919 

